Radio transmission system



March 24, 1925. 1,53w29 F. M. RYAN RADIO TRANSMISSION SYSTEM Fi1ed A ug.24, 1921 LPF T,

M van for: Franc/'5 M Ryan Patented Mar. 24, 1925 UNIT D STATES PATENTounce.-

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Application filed August 24, 48:21.- Serial No. (915,026i

To allwkomz't may concern:

Be itknown that I FRANCIS M. RYAN, a citizen of the United tates,residin at East Oran e, in the county of Essex, tate of I New ersey,have invented certain new and useful Improvements in Radio TransmissionSystems, of which the following is a full, clear, concise, and exactdescriptlon.

This invention relates to radio transmis- .1 sion systems and moreparticularly to arrang'ements for excluding interfering energytherefrom.

A feature of the inventionconsists in the provision of a reactive trapcircuit having extremely large impedance for undesired energy, but lowimpedance for energyof the deslred frequency.

Another feature of the invention relates to the association. of areactive trap circuit with a loop receiving antenna in such manner as topermit the loop to have the greatest possible effective receivinginductance.-

It is customary in duplex radio signaling to use different carrierfrequency waves for outgoing and incoming transmission, in .order topermit the receiving apparatus to discriminate against the locallyradiated wave. An additional feature of the present invention consistsin increasing the discrimination of the receivin apparatus againstlocally radiated waves y lncluding therein a trap circuit which offershighimpedance to these locally radiated waves.

According to this invention, a radio receiving system is provided withan antiresonant or tuned loop circuit tuned to the frequency of thecarrier wave radiated b the local radio transmitting station and th foreserving to substantially exclude the lo 40 cally radiated energy fromthe receiving system. A 100 antenna is used and if the frequency of tielocally radiated carrier wave is lower than that of the received wave,the

trap circuit is placed in the primary receiving circuit in series withthe loop antenna.

If the frequency of the locally radiated carrier wave 1s higher thanthat of the received wave, the trap circuit is placed in the secondarycircuit which is coupled to the pri.

mar circuit.

T e novel features which areconsidered characteristic of the inventionare set forth with particularity in the appended claims. The inventionitself, however, both as to its -qrganization and method, of operation,to

ere-

gether with further objects and-advantages" thereof, will best beunderstood by reference to the following description taken in connectionwith the accom anying drawing in which Fig. 1 illustrates ia ammaticallythe circuit arrangements whic ma be employed at one terminal of a radioto 1 linkin carrying'the invention into effect, and Fig. 2

the circuit arrangements at the other terminal of the same radio tolllink.

Referring to Fig. 1, a signaling station I which may represent a localoperators station, a central exchange, or.a subscribers station,connected through an exchange, is associated with a line L, whichconnects thesignaling station with the incoming and out going radiochannels 3 and 4 by means ofthe well-known balanced transformer or hbrid coil 6 and the balancing network The outgoin radio channel togetherwith the transmi ting apparatus T, and radiatin antenna 11, andtheincoming radio chan'ne together with receiving antenna 12, 'consti: tutethe radio apparatus at one terminal of a radio t'olll-inkconnecting thestation 1 with 80 a distant station.-

The outgoing radio channel 4 includes an amplifier A, preferablyalthough not necessarily of the well-known three-element vacuum tubetype and a low pass filter LPF from which the signaling. currents orimpulses originating at station 1 are 'transmitted to radio transmittingapparatus '1, to cause correspondingly. modified; oscillations offrequency F, to be supplied to trans mitting antenna 11 and radiatedtherefrom.- The network N as in the ordinary case, is so desi ned as tosimulate the impedance oi line and its associated station at thefrequencies of all of the currents transmitted over line L,. The lowpass filter LPF may be of the general type described in the articleCarrier current telephony and telegraphy at pages 311 and 312 of theJournal of the American Institute of Electrical Engineers, volume 40,No. 4, April 1921.

. ance of the primary circuit to the fullest adjacent or may beseparated by a distance of several miles. It IS desirable to .make theeffective receiving inductance of the antenna loop as great as possibleand to tune the antennal circuit .as a whole to the frequency F, of theincoming oscillations. This requires that-trap 'circuit- 15 shouldpresent a capacity rea'ctance at the frequency F or in other words, thatthe frequency of the incoming waves be higher than that of the locallyradiated waves. It is accordingly possibleto utilize the inductadvanta ein the antenna loop'itself. Tuning of the primary circuit to thefrequency F 2 is accomplished by means of the varlable capacity element13.

- Incoming oscillations received by the antenna or primary circuit areapplied by means of transformer 14 to the secondar circuit 16 also tunedto the frequency and are impressed upon a demodulator D together withoscillations of high frequency F supplied by a'local oscillator 0.Demodulator D which may be of. any desired type functions in the samemanner as the similarly designated element of- United States patent toOsborne 1,361,487, patented December 7, 1920, to yield in its outputcircuit intermediate frequency oscillations of the frequency F,Fmodulated or otherwise modified in the same manner as the receivedoscillations of frequency F The intermediate frequency oscillations areamplified by an intermediate frequency amplifier IF A which may includee1ther a band pass filter or a-lowpass filter of the types described inthe article Carrier current telephony and telegraphy previouslymentioned. The amplifier and filter are designed to transmitoscillations of a band of frequencies of an extent at least equal tothat of the original signaling currents by which the incoming carrierwave of frequency F is modified. The intermediate frequency oscillationsafter modification and selection are impressed upon a second demodulatorD which serves to derive therefrom waves of the original signal currentfrequencies which after modification by an amplifier A and selection bya low pass filter LPF, similar to that in channel 4 are impressed uponline L and transmitted to station 1.

Upon reference to Fig. 2 it will be noted that the arrangement andoperation of the apparatus at the remote terminal of the radio toll linkare in general the same as in the case of the terminal apparatusillustrated in Fig. 1. The statlon 2 which is connected by the radiotoll link to station 1 is associated with a line L,, radio transmittingapparatus T receiving channel3 and transmitting channel 4, similar tothose of Fig. 1. The frequency of the carrier wave .F,-F and in thatcase the cements connected between the demodulator D and the hybrid coil6 in receivin channel 8 of Fig. 2- may be exactly like t e similarlydesignated elements in receiving channel 3 of Fig. 1. If F does not havethe particular value stated above, the apparatus in the receivingchannel 3 of Fig. 2 will vary only in that it is particularly designedto transmit an intermediate frequency carrier wave of frequency F ,F,.The frequency F of 1 radiated carrier wave is higher the locall than therequency F of the received waves. A trap circuit 25 comprising a closedloop tuned to the frequency F is connected in series in the closedsecondary circuit 26 which is tuned to the frequency F of the receivedcarrier waves. This trap circuit ofi'ers anlnductive reactance atfrequency F and if introduced directly'into the primary circuit of theloop antenna 22, would diminish by a certain amount the effectiveinductance which might otherwise be given the antenna loop. Thearrangement of the trap circuits at the two stations permits each loopantenna to have the greatest ossible effective receiving inductance andcos not nterfere with sharp selectivity for the carrier wave to bereceived as has been demonstrated in practice.

In a given example, the frequencies F F F and F may have the magnitudes600 kilocycles, 750 kilocycles, 700 kilocycles and 50 kllocyclesrespectively. The intermediate frequency at each terminal will then be50 kilocycles. If the system is used for speech transmission, theintermediate frequency amplifier and any selective circuits associatedwith it must then be capable of transmltting a band of currents at leastas extensive as one side band of a speech modulated wave having acarrier frequency of 50 kilocycles.

The anti-resonant circuit ofi'ers substantially infinite impedance tocurrents of one frequency and very high impedance to currents of aconsiderable range of frequencies adjacent thereto. Energy offrequencies not substantially suppressed by the antiresonant circuit maybe combined by the demodulator D with oscillations from the localoscillator to produce difference frequency oscillations. Theseoscillations will, however, be excluded by the selective cirpiuits ofthe intermediate frequency ampli- Although the invention has beendescribed as embodied in a specific radio transmission system, it iscapable of use generally in high frequency wave transmission. It isthereundesired frequency.

prising a closed energy-receiving circuit, a-

secondary circuit coupled thereto and" tuned to waves of a desiredcarrier frequency, and

means having inductive reactance at desired frequencies in saidsecondary circuit for excluding energy of undesired frequency.

3. A radio receiving system comprising a closed antenna circuit, asecondary circuit connected thereto, and meanshavin'g inductivereactanceconnected-in one side of said secondary circuit for excludingenergy of 4. A radio receiving system comprising a closed antennacircuit, a secondary circuit coupled thereto and tuned to waves of thedesired carrier frequency, and means hav ng inductive reactanceconnected in one side only of said secondary circuit for excludingenergy of undesiredfrequency.

5. A radio receiving system COIIIPIlSlng a closed antenna circuit, asecondary circuit connected thereto and a closed loop having inductivereactance at desired frequencies 1n said secondary circult anti-resonantat the frequency of undesired waves for excluding said undesired waves.

6. A radio receiving system comprising a closed antenna circuit, asecondary circuit coupled thereto and tuned to the waves of the desiredcarrier frequency, and a closed loop having inductive reactance atdesired frequencies in said secondary circuit anti-resonant at thefrequency of .undesired waves for excluding said waves.

7. A radio receivin system comprising an antenna circuit inc uding aloop antenna, a secondary circuit connected thereto, and a closed loopinductively reactive at desired frequencies connected in series in saidsecondary circuit andtuned. to the frequency of waves which it isdesired to exclude.

8. A radio receivin system comprising an antenna circuit inc uding aloop antenna, a secondary circuit coupled thereto and tuned to waves ofthe desired carrier fre quency, and a closed loop having inductivereactance at desired frequencies in series in said secondary circuit andtuned to the frequency of waves which it is desired toexclude.

9.. A radio receiving system comprising a closed antenna circuit, asecondary circuit connected thereto, a radio transmitting. station fortransmitting waves of a frequency v ceive, and means havin other thanthat which it is desired to reinductive reactance at desired frequenciesin said secondary circuit for excluding waves transmitted from saidradio transmitting station.

10. A radio receiving system comprising a circuit including a loopantenna, a secondary circuit coupled to said first named circuit andtuned to wavesof the desired carrier frequency, a radio transmittingstation for transmitting waves of a frequency other than that which itis desired to receive, and means in said secondary circuit comprising aclosed loop having inductive reactanceat desired frequenciesanti-resonant at the frequency of the wavestransmitted from saidtransmitting station for excluding said waves.

11. A low'frequency transmission line, a radio transmitting .station'for transmitting carrier waves modified in accordance with electricalimpulses transmitted over said line, a radio receiving stationcomprising a closed antenna circuit, a secondary circuit coupled theretoand tuned to waves of a carrier frequency other than thatof said radiotransmitting station, a closed loop in said secondary circuitanti-resonant at the frequency of the waves transmitted from said'transmitting station, and means for impressing upon said line impulsesobtained by demodulating the waves received by said radio receivingstation.

12. A radio toll link comprising transmitting and receiving apparatusconstitut a channel.

13. A radio toll link comprising transmitting and receiving apparatusconstituting two channels for oppositely directed transmission, onechannel being selected for carrier waves of one frequency and the otherchannel for carrier waves of a different frequency, a tuned receivingcircuit in the lower frequency channel, a secondary circuit coupled tosaid receiving circuit, a loop antenna in said receiving circuit, and

a loop anti-resonant at the high carrier frequency in said secondarycircuit.

14. 'A radio toll link comprising two oppositely directed radiotransmission channels, one channel being selective for carrier waves ofone frequency and the other channel for carrier waves of a differentfrequency each channel comprising a primary receiving circuit and asecondary receiving circuit coupled thereto, each of said primarycircuits including a loop antenna, and

a closed loop anti-resonant at thecarrier frequency of the oppositelydirected channel in the primary circuit of'one channel and in thesecondary circuit of the other channel.

15; In a radio receiving system, an antenna impressed with desired andundesired waves, a secondary circuit coupled to said antenna, a detectorand a receiving device and means in said secondary circuit 7 includingan inductance and acapacit'y for excluding waves of undesired frequencyfrom said receiving device, the reactance of said inductance being suchas to predominate over the reactance of said capacity at the frequencyof desired waves.

In witness whereof, I hereunto subscribe my name this 5th day of AugustA. D.,

FRANCIS M. RYAN.

